It is known that a patrol of aircraft, for example of fighters or military transporters, is composed of a lead aircraft, also called the leader, which is followed in flight according to a particular spacing (defined vertically, longitudinally and laterally) by one or more follower aircraft, also called wingmen. The relative flight between the lead aircraft and a follower aircraft may be performed:                either simply (and exclusively) on the basis of the judgment of the pilot of the follower aircraft, as a function of his direct vision of the lead aircraft;        or by way of a system of information and/or for aiding piloting, such as an electronic system for aiding a patrol flight.        
During a patrol flight, the aircraft follow one another while attempting, in particular, to constantly maintain one and the same longitudinal gap. This longitudinal gap which represents a distance-wise objective, may be expressed, when the flight is managed with the aid of an electronic system for aiding a patrol flight:                either as a unit of distance (for example meters), calculated along the flight trajectory of the lead aircraft;        or as a unit of time (for example seconds), corresponding to the division of the distance by the speed of the follower aircraft (or of the lead aircraft). In this case, the longitudinal gap also relates to a distance, but it is expressed indirectly through a unit of time.        
Consequently, the longitudinal gap taken into account during a standard patrol flight always corresponds to a distance.
A standard patrol flight such as this thus exhibits several drawbacks. In particular:                it requires a very fast reaction of the one or more follower aircraft, so as to constantly maintain the same distance with the lead aircraft. However, an aircraft and its systems inevitably exhibit inertia and a reaction time, this possibly giving rise to concertina effects and risks of instability, in particular in the case of long patrols comprising numerous follower aircraft;        it implies that a variation in speed of the lead aircraft must necessarily be applied simultaneously to all the follower aircraft, this sometimes possibly being incompatible with the flight trim, in particular if not all the aircraft are in the same flight phase at the current instant.        